The present invention relates to drainage tiles in general, and to drainage tiles constructed of plastic in particular.
Although perhaps little noticed, drainage pipes or passageways have an ancient history and an important role in supporting the structures upon which civilization is built. A buildup of water within soil can reduce the bearing strength of the soil. A buildup of water can also create large hydraulic forces behind a wall or beneath a road or pavement. Engineers from ancient times have utilized ditches and passageways constructed of stone, wood, and tile to drain water away from foundations, roadways, and fields.
Materials which are utilized for forming drainage passageways should typically be resistant to rot, particularly where used to drain water away from foundations and roadways where the useful life of the structure may be decades or even centuries. Thus the typical materials used have been stone, ceramic tile, and concrete.
Recently plastic has found utility in drainage applications. While plastic may not necessarily be considered as durable as ceramic tile or concrete, in many practical circumstances its inherent properties, including light weight and durability, result in substantial advantages over more traditional materials. The great weight of ceramic and concrete drainage tiles increases the cost of transportation and the difficulty of handling and placing drainage structures. Ceramic tile and, to a lesser extent concrete, are subject to brittle fracture. Although not necessarily always considered in the design of drainage structures, in many real-life situations drainage structure failure is due to impact damage when the structures are dropped. Crushing damage occurs when drainage structures are accidentally driven over, by heavy equipment either before or after placement.
With the advent of the recycle culture, large quantities of certain plastics, particularly polyethylene, have become available. The availability of recycled materials has meant it is cost-effective to use such materials in heavy sections, even where low cost is a consideration.
Plastic as a material of construction finds particular utility in highway underdrain apron end walls. Apron end walls are the structures which receive water from drainage pipes placed under highways to prevent the buildup of water within the foundation of the highway. Thus the apron end walls are exposed at the sides of the road leading into drainage ditches. Their exposure means they are often run over by heavy equipment and at times struck by mower blades. If they are constructed of plastic they are much less subject to damage by heavy equipment and at the same time cause less damage to the mower blades.
Traditional materials used in the fabrication of drainage structures are substantially more dense than water, however plastic tends to be slightly less dense than water. The lower density of plastic means that in a saturated soil, or under flooded conditions within a drainage ditch, it is possible that the buoyant force on an apron end wall could cause an apron end wall to be displaced from its designated position.
What is needed is a plastic aproned end wall which resists movements due to buoyancy forces.
The plastic apron end wall of this invention incorporates lateral wings which extend out from the sides of the apron end wall so that, as installed, the soil overburden prevents the apron end wall from being displaced upwardly by buoyancy forces in the event the ditch into which the apron end wall drains becomes flooded. The lateral wings extend outwardly from the sides of the apron end wall into the soil which surrounds the sides of the apron. The total planar area of the wings is selected so that the overburden, that is the soil which lies above the wings, is sufficient to offset any buoyancy force produced by water saturating the soil in which the apron end wall is embedded.
It is an object of the present invention to provide a plastic apron end wall which is resistant to buoyant forces.
It is a further object of the present invention to provide an apron end wall which accommodates being constructed of plastic or other lightweight material.
Further objects, features and advantages of the invention will be apparent from the following detailed description when taken in conjunction with the accompanying drawings.